Determination of phosphorus-containing compounds by spectrophotometry

No single method has been applicable for the determination of total phosphorus in the large spectrum of naturally-occurring and synthetic phosphorus-containing compounds, especially for those of extreme stability; e.g., ionic 0,O-dialkyl phosphates and 0-alkyl alkylphosphonates; the available phosphorus assay procedures determine only certain classes of phosphorus compounds. Phosphate esters from cells and tissues have been assayed routinely for total phosphorus after acid hydrolysis (e.g., 1) . Nonesterified alkylphosphonates have been determined after alkaline persulfate oxidation ( 2 ) ; however, 0-alkyl alkylphosphonates are not hydrolyzed quantitatively (3) , and the detection limit and the sensitivity in these determinations are poor (30-1600 nmol/assay). We have found (Cook and Daughton, unpublished data) that dry ashing with 5 M "OB ( 4 ) results in incomplete and erratic recovery of dihydrogen 2-aminoethylphosphonate as orthophosphate. Subsequently, we found that a published method for wet ashing of aminoalkylphosphonates ( 5 ) could be extended and modified to give a simple, safe, general procedure for nongaseous phosphorus compounds in the 1-50 nmol range: this new procedure is described here. The orthophosphate resulting from the ashing was assayed by the highly sensitive method of Bartlett ( I ) .